A quality control engineer is in charge of the manufacturer of USB thumb drives. Two different processes can be used to manufacture the thumb drives. He suspects that the Kohler method produces a greater proportion of defectsthan the Russell method. He samples 130 of the Kohler and 180 of the Russellthumb drives and finds that 27 and 18 of them, respectively, are defects.

a. Perform an appropriate test at a level of significance of 0.01 to confirm the suspicion of the engineer.

b. Construct a 95% confidence interval estimate for the difference between the proportion of defect thumb drives produced by Kohler andRussell method and interpret it.